In the operation of various devices such as internal combustion engines, air compressors, and like machinery, undesirable torsional vibration on the rotating members will be present. There will also be present a degree of radial and angular vibration depending on the number and arrangement of components undergoing linear and oscillatory motion. In the case of internal combustion engines where the revolutions per minute can vary over a wide range, it is particularly difficult to directly and flexibly couple the output shaft member to an input shaft member which has a considerable moment of inertia and, at the same time, avoid resonant harmonic frequencies between the input and output members in applications where the magnitude of oscillation at resonance can be destructive. This problem becomes particularly critical where design criteria demand the use of a single cylinder, two-cycle engine that yields maximum horsepower for minimum weight in order to provide hand portability without vibrations beyond the coupling.
In these applications, there will be a minimum mass of crankshaft flywheel and counterweights and the engine RPM may inadvertently exceed 15,000 . Further, the engine itself will be suspended within and isolated from the unit frame and all other components by means of very flexible rubber mounts. Thus, the engine output shaft member is free to oscillate torsionally, radially, angularly, and axially with respect to the frame-mounted driven shaft member. Furthermore, the magnitude of these oscillations vary somewhat independently of each other as engine RPM and engine load vary independently. Resonant frequencies, harmonics, and parasitic oscillations may not always occur at specified points of engine RPM because of a varying engine load at these specified points. Thus, there is a need in the art to provide a flexible coupling which will operate under these critical conditions.